docs: def export(self, nidm_version, export_dir):
          """
          Create prov graph.
          """
          # Contrast Map entity
          atts = (
              (PROV['type'], NIDM_CONTRAST_MAP),
              (NIDM_CONTRAST_NAME, self.name))
  
          if not self.isderfrommap:
              atts = atts + (
                  (NIDM_IN_COORDINATE_SPACE, self.coord_space.id),)
  
          if self.label is not None:
              atts = atts + (
                  (PROV['label'], self.label),)
  
          if self.name is not None:
              atts = atts + (
                  (NIDM_CONTRAST_NAME, self.name),)
  
          # Parameter estimate entity
          self.add_attributes(atts)